1. Field of the Invention
The present invention relates to oil and gas well testing and, more particularly, but not by way of limitation, to method and apparatus for safely testing and sampling potentially hazardous well fluids in hostile environments.
2. Description of the Prior Art
In the past, formation testing has been employed to determine the potential productivity of subsurface formations in either open or cased well bores. The prior art testing procedures requires the opening of a section of the well bore to atmospheric or reduced pressure. The prior art method has previously been accomplished by lowering a test string into the well bore on drill pipe with the tester valve closed to prevent entry of well fluid into the drill pipe. With the packer of the testing string expanded to provide a seal above the zone to be tested, the tester valve is opened. The packer is then relied upon to support the hydrostatic pressure load of the well fluid. The formation below the packer is relieved of this pressure and is exposed through the open tester valve to the atmospheric pressure in the empty drill pipe so that its ability to produce fluid can be determined.
After a specified time interval, the formation is closed in to measure its rate of pressure build-up.
At the end of the test the tester valve is closed and pressure is equalized across the packer to permit it to be unseated. Formation fluid recovered during the test can be removed from the drill pipe by reverse circulation before the pipe is removed from the hole. Formation pressures are generally recorded throughout the test by a subsurface pressure recording device included in the testing string.
Such prior art formation testing techniques are not appropriate for extremely deep wells where formation pressures of approximately 20,000 p.s.i. and temperatures of approximately 500.degree. F. may be encountered. Safety considerations prevent the venting of such formation pressures to the atmosphere as is common practice in the prior art. This limitation of the prior art method and apparatus is particularly apparent when H.sub.2 S or CO.sub.2 is a substantial component of the well fluids encountered in the zone under test.